Ventricular assist devices, known as VADs, often include an implantable blood pump and are used for both short-term (i.e., days, months) and long-term applications (i.e., years or a lifetime) where a patient's heart is incapable of providing adequate circulation, commonly referred to as heart failure or congestive heart failure. According to the American Heart Association, more than five million Americans are living with heart failure, with about 670,000 new cases diagnosed every year. People with heart failure often have shortness of breath and fatigue. Years of living with blocked arteries and/or high blood pressure can leave a heart too weak to pump enough blood to the body. As symptoms worsen, advanced heart failure develops.
A patient suffering from heart failure may use a VAD while awaiting a heart transplant or as a long term destination therapy. A patient may also use a VAD while recovering from heart surgery. Thus, a VAD can supplement a weak heart (i.e., partial support) or can effectively replace the natural heart's function.
The flow rate of blood pumped by a VAD is an important parameter for both control of the blood pump and for informing a health care professional regarding the level of circulatory support provided to the patient by the VAD. Direct blood flow rate measurement, however, may be undesirable with respect to additional components, such a flow rate sensor, that would be used to directly measure the flow rate of blood pumped by the VAD. Such additional components may add to the complexity and size of the VAD, thereby potentially making the VAD more expensive and occupy more space within the patient. Additionally, a flow rate sensor may increase the rate of thrombosis (blood clot formation) as a result of the interface between the flow rate sensor and the blood flow.
In view of the challenges associated with direct blood flow rate measurement in a VAD, flow rate in a VAD may be estimated. For example, the blood flow rate in a VAD can be estimated based on the amount of electrical power consumed by the VAD. For some operational regimes of a blood pump, however, estimated flow rate based on electrical power consumed by the VAD may not be sufficiently accurate. As such, improved approaches for estimating blood flow rate in a VAD are desirable.